dt-binding: memory: pl353-smc: Describe the child reg property

Each chil node should have a reg property, no matter the type of
controller (NAND, NOR, SRAM). This should be part of the bindings.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210610082040.2075611-5-miquel.raynal@bootlin.com


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>